Important Questions

Which organelles have a double membrane and their own DNA?

Mitochondria and chloroplasts, which have double-membranes and their own DNA, are believed to have originated from incompletely consumed or invading prokaryotic organisms, which were adopted as a part of the invaded cell.

· What are cell membranes made out of?

All living cells and many of the tiny organelles internal to cells are bounded by thin membranes. These membranes are composed primarily of phospholipids and proteins and are typically described as phospholipid bi-layers.

How do the non-polar hydrophobic tails/polar hydrophilic heads in a phospholipid play a role in cell membrane formation?

Cells exist in an aqueous environment. The hydrophilic heads of the phospholipids interact with this aqueous environment, since they are polar. The hydrophobic ends are oriented away from this environment. Due to this, a bilayer can be formed ( a double layered sheet formed by phospholipids where the hydrophobic end are directed inwards towards the opposite side of the aqueous environment and its hydrophilic end directed outwards)

How are peripheral and integral proteins different?

Peripheral membrane proteins, or extrinsic proteins, do not interact with the hydrophobic core of the phospholipid bilayer. Instead they are usually bound to the membrane indirectly by interactions with integral membrane proteins or directly by interactions with lipid polar head groups.

A phospholipid?

Phospholipids consist of a glycerol molecule, two fatty acids, and a phosphate group that is modified by an alcohol. The phosphate group is the negatively-charged polar head, which is hydrophilic. The fatty acid chains are the uncharged, nonpolar tails, which are hydrophobic.

What is a lipid bilayer?

The lipid bilayer is a thin polar membrane made of two layers of lipid molecules. These membranes are flat sheets that form a continuous barrier around all cells.